Railroad crossing gate arms are lowered from a vertical position to a horizontal position to block traffic from crossing railroad tracks when a train is present. When lowered to their horizontal position, gate arms can suffer damage from passing vehicles, wind pressure and vandalism. Damage frequently results in broken gate arms that sever at their point of attachment to a crossing gate mechanism. Such damage risks exposing pedestrians and vehicular traffic to improperly guarded train crossings. To maintain safety and the integrity of grade crossing equipment, railroads expend substantial resources monitoring, repairing and replacing damaged crossing gates. Thus, in the first instance, it is advantageous to protect lowered gate arms from damage.
Various methods of protecting gate arms from damage were known to the prior art. Employing camblocks and ball bearings, U.S. Pat. No. 4,897,960 issued to Barvinek, et al., (hereinafter referred to as "Barvinek") describes a mechanism designed to provide flexibility to lowered gate arms. Barvinek discloses a housing for pivotally mounting a support tube that swings a partially translucent, internally illuminated, impact-resistant gate arm away from an applied force. A camblock is mounted inside the housing, allowing the gate arm support tube, having a pair of ball bearings retained within, to rotate around a retaining pin that extends upwardly through the center of the camblock when force from a passing vehicle is applied. Downward force on the rotating gate arm support tube, applied by a coil spring mounted on the retaining pin, forces the arm to return to its original position parallel with the groove of the camblock when the force dissipates. However, Barvinek suffers from numerous problems. Relying on camblocks and ball bearings, Barvinek is expensive to manufacture, monitor and maintain. Moreover, Barvinek cannot return a displaced gate arm to a position parallel with the groove of the camblock if the gate mechanism rises while the gate is displaced. Finally, Barvinek provides no control over the rate of gate arm return and cannot prevent gate arm over travel into the flow of traffic.
Alternatively, U.S. Pat. No. 5,469,660, issued to Tamenne, (hereinafter referred to as "Tamenne") employs a spring and hydraulic piston system. Tamenne discloses a pivot assembly allowing a lowered gate arm to rotate away from traffic when a passing vehicle applies pressure and then to return to its original position once pressure is removed. The pivot assembly is mounted on a counter-weighted gate arm mechanism and includes springs mounted on a shuttle post assembly to return the gate arm to a position perpendicular to the flow of traffic. The pivot assembly includes a hydraulic piston to buffer the rate of gate arm return and a weight channel to counterbalance the gate mechanism's main counterweight when the gate arm is rotated away from passing traffic. However, Tamenne also suffers from numerous problems. Tamenne's hydraulic piston system, like Barvinek's camblock and ball bearing system, is expensive to manufacture, monitor and maintain. Further, Tamenne's weight channel counterbalance places an imbalanced strain on the gate arm pivot assembly, risking damage to the gate arm mechanism. Tamenne also decreases safety at crossing grades when the gate arm is displaced, because the weight channel swings from a position generally parallel with the flow of traffic to a position generally perpendicular to the flow of traffic and through an area where pedestrians may be standing. Like Bamivek, Tamenne is incapable of returning a displaced gate arm back to its normal position if the gate mechanism rises while the gate is displaced.
Therefore, a need exists for a crossing gate mechanism that can rotate a crossing gate arm out of the way of a damaging force while safely and efficiently returning the gate to its normal position, that is capable of being adjusted for installation in conditions requiring varied gate arm lengths and flexibilities, that is capable of preventing excessive impact when the gate arm returns to its normal position, that prevents gate arm over travel upon return from a displaced position, that is capable of being adjusted for varying gate arm return force requirements, that is less expensive than existing spring-based crossing guard mechanisms, and that is not subject to the potential for deterioration of a cam-and-bearing based crossing gate mechanisms.